The present invention relates to a diaphragm pumping apparatus; more particularly, the invention relates to a double diaphragm pump having a two-stage air valve actuator for regulating the pumping action.
Double diaphragm pumps are well known in the art, wherein a source of pressurized-air is selectively applied into each of two diaphragm chambers to thereby cause deflection of the respective diaphragms to create a pumping action against liquid materials which are introduced into the diaphragm chamber. Each diaphragm effectively isolates the chamber into two halves, a first half which is susceptible to varying air pressures and a second half which is exposed to the liquid materials being pumped.
The delivery of pressurized air to a double diaphragm pump is typically controlled by an air valve, and the air valve is typically actuated by a mechanical linkage to the diaphragms. Therefore, deflection of one diaphragm causes the actuator to toggle the air valve so as to introduce pressurized air into the diaphragm chamber, which then causes deflection of the second diaphragm until the mechanical actuator toggles the air valve in the reverse direction. This reciprocating movement of the respective diaphragms continues for so long as the pressurized inlet air exceeds the pressure of the liquids confined in the delivery portion of the diaphragm chambers. When the liquid and air pressures equalize, the diaphragms no longer cycle and the pump undergoes what is referred to as a stall condition. This stall condition exists until a pressure imbalance occurs, and the air pressure driving force against the diaphragm again causes diaphragm movement. The valve actuator which controls the flow of pressurized air into the diaphragm chambers is typically mechanically linked to the diaphragms themselves, so as to become actuated at predetermined positions of the diaphragm. In some cases, double diaphragm pumps have utilized a pilot valve mechanically linked to the diaphragm, which then directs the flow of pressurized air to an actuator valve, and the actuator valve directs the flow of pressurized air to the diaphragm chamber. Various types of spool valves have been utilized for either or both of these valving functions.
The actuator valve which functions to direct the flow of pressurized air into a diaphragm chamber usually simultaneously exhausts the pressurized air from the other diaphragm chamber. The air exhausting through the valve actuator undergoes rapid and sudden decompression, causing a dramatic drop in temperature in the proximity of the valve actuator. Repeated exhaust cycles, particularly when the pressurized air has significant moisture content, results in frost buildup proximate the actuator valve and in the exhaust chamber. This frost buildup can accumulate and create an icing effect, which in the extreme can block the further physical movement of the actuator valve and thereby disable the pumping system.
Another problem with prior art double diaphragm pumps relates to the inefficiencies caused by wear of the valve actuators. Valve actuators typically cycle at rates up to several hundred times per minute during the lifetime of the pump, and as these actuators gradually wear, the air seals associated with the actuators undergo leakage which degrades the pressurized operation of the pump. This can eventually lead to pump failure when the leakage condition becomes so excessive as to no longer permit the actuators to operate effectively.